Network Simulator, NS-2 Blog

Apr 8, 2010

BitTorrent is one of the Internet's most efficient content distribution protocols. It is known to perform very well over the wired Internet where end-to-end performance is almost guaranteed. However, in wireless ad hoc networks, many constraints appear as the scarcity of resources and their shared nature, which make running BitTorrent with its default configuration not lead to best performances. To these constraints it adds the fact that peers are both routers and end-users and that TCP-performance drops seriously with the number of hops. We show in this work that the neighbor selection mechanism in BitTorrent plays an important role in determining the performance of the protocol when deployed over a wireless ad hoc network. It is no longer efficient to choose and treat with peers independently of their location. A first solution is to limit the scope of the neighborhood. In this case, TCP connections are fast but there is no more diversity of pieces in the network: pieces propagate in a unique direction from the seed to distant peers. This prohibits peers from reciprocating data and leads to low sharing ratios and suboptimal utilization of network resources. To recover from these impairments, we propose an enhancement to BitTorrent which aims to minimize the time to download the content and at the same time to enforce cooperation among peers. Our solution considers a restricted neighborhood to reduce routing overhead and to improve throughput, while establishing few connections to remote peers to improve diversity of pieces. With the help of extensive NS-2 simulations, we show that these enhancements to BitTorrent significantly improve the file completion time while fully profiting from the incentives implemented in BitTorrent to enforce fair sharing.

The Mannasim Framework is a module for WSN simulation based on theNetwork Simulator (NS-2). Mannasim extends NS-2 introducing new modules for design, development and analysis of different WSN applications.

The Script Generator Tool (SGT) is a front-end for TCL simulation scripts easy creation. SGT comes blunded with Mannasim Framework and it's written in pure Java making it plataform independent.

Mannasim Objectives

Mannasim goal is to develop a detailed simulation framework, which can accurately model different sensor nodes and applications while providing a versatile testbed for algorithms and protocols.

Numerous challenges make the study of real deployed sensor networks very difficult and financially infeasible. At the current stage of the technology, a practical way to study WSNs is through simulations that can provide a meaningful perspective of the behavior and performance of various algorithms.